1. Field of the Invention
This invention relates to a plant for producing steel and more particularly to an improved fluidized bed plant for producing steel directly from iron ore fines using coal and oxygen to reduce and melt the ore fines.
2. Description of the Prior Art
Steelmaking is presently carried out by two major routes. The first is the traditional coke oven/blast furnace/basic oxygen converter method which relies upon pellets, lump, or sinter ore, coking quality coal, and oxygen to produce steel. The second method utilizes the electric arc furnace to melt down and purify scrap metal and in some cases directly reduces iron by electric current to form steel.
The disadvantage of the blast furnace method is that such plants require vast capital expenditures, that high quality coking coal is required, and that atmospheric emissions are high and plants require extensive pollution control systems in order to meet present air quality standards.
The electric furnace method on the other hand relies upon electric power for the heat of fusion and cannot utilize coal. This limits its use to areas with large industrial electric grids due to the high power consumption. Additionally the cost of the energy supplied by electric is generally higher than that supplied by fossil fuel sources, such as coal. The furnaces cannot utilize iron ore directly, but must have either good quality scrap or a pre-reduced iron ore as a feedstock.
In order to perfect a more efficient steelmaking process, recent research and development has been centered upon direct steelmaking wherein raw iron ore is fed into a process which utilizes coal and oxygen to first provide a reducing gas to pre-reduce the ore and secondly to provide the heat required to melt the pre-reduced ore to make liquid iron. The iron product usually requires a subsequent refining step to reduce impurities contained in the iron and to adjust the carbon level of the steel prior to casting.
These direct steelmaking processes have important potential advantages or lower capital investment, lower atmospheric emissions and use of low quality, non-coking coal when compared to the coke oven/blast furnace plants, and the ability to use coal as a power source and to process raw iron ore directly when compared to the electric furnace process.
Some of the further disadvantages of the present direct steelmaking processes are that many require iron ore to be in the pellet, lump, or sinter form and cannot use iron ore fines directly. These coarser forms of iron are more costly than iron ore fines; and, the sinter and pellet forms require an additional processing step. Often the processes produce an excess of reducing gas which has to be burned in a separate facility as fuel gas. Since the gas has potential to be used as a reducing gas, there is an overall loss of process efficiency when it is burned, and hence an increased cost of steel.
Accordingly, there is a need for a steelmaking plant and/or process which has the known advantages of direct use of iron ore and use of lower quality coals, reduction of energy consumption, lowering of capital costs, and reduction of atmospheric emissions. Further the process should improve upon present direct steelmaking processes by using iron ore fines, and fully utilize the reducing gas produced in the process.